Electron discharge tube circuit arrangement, including selective and nonselective negative-feedback means and selective positive-feedback means



Dec. 4, 1951 J. A. GREEFKES ETAL 2,577,461

ELECTRON DISCHARGE TUBE CIRCUIT ARRANGEMENT, INCLUDING SELECTIVE AND NONSELECTIVE NEGATIVE-FEEDBACK MEANS AND SELECTIVE POSITIVE-FEEDBACK MEANS Filed Feb. 20, 1948 AAAAAA VVVVVY l v I N V EN TORS. JOHANNES ANTON GREEFKES BY JOHANNES ENSLNK A GEN If Patented Dec. 4, 1951 ELECTRON DIS CHARGE TUBE CIRCUIT AR- RANGEMENT, INCLUDING SELECTIVE AND NO N S ELE C TIVE NEGATIVE-FEEDBACK MEANS AND SELECTIVE POSITIVE-FEED- BACK MEANS Johannes Anton Greefkes and Johannes Ensink, Eindhoven, Netherlands, assignors to Hartford National Bank. and Trust Company, Hartford,

Conn.,, as trustee Application February 20, 1948, Serial No. 9,856 In the Netherlands March 4, 1947 7 Claims. (01. 250-36) The invention relates to a circuit-arrangement comprising a discharge tube, with which positive feed-back, selective for a definite frequency, is provided between the anode circuit andthe control-grid circuit and this discharge tube is negatively fed back for all frequencies.

As is well known, such circuit-arrangements may be used, for example, in oscillators, in which event the stability of the frequency of the oscillations produced by the oscillator may be appreciably enhanced.

However, these circuit-arrangements have the disadvantage that, if greater stability is required, the value of the negative feed-back must be modified, which involves that also the amplitude of the alternating voltage produced by the oscillator varies.

The circuit-arrangement according to the invention obviates this disadvantage. and exhibits the feature that negative feed-back selective for the same definite frequency, exists between a circuit which is connected to an additional grid of the discharge tube and to which a positive voltage is supplied, and the control-grid circuit.

The operation of such a circuit-arrangement is based on the recognition that with an increasing amplitude of the alternating voltage in the anode circuit the average anode current decreases and the average current flowing to a grid present in the tube and having a positive voltage supplied to it, for example, a screen-grid, increases.

Owing to the decrease of the average anode current, and consequently of the mutual conductance, the positive feed-back decreases, whereas the mutual conductance in the other circuit and hence the negative feed-back increase, limitation of the amplitude of the alternating voltage in the anode circuit being thus obtained.

The cathode current of the discharge tube is, in first approximation, equal to the sum of the currents flowing to the anode and to the screen grid and hence independent of the current distribution occurring between these two electrodes, so that, if the negativefeed-back for all frequencies is taken from a resistance included in the cathode lead, this negative feed-back does not vary with varying current-distribution.

Moreover, with variation of this resistance, in which event the negative feed-back for all frequencies and hence the frequency stability of the arrangement vary, within certain limits, variation of the amplitude of the alternating voltage in the anode circuit does not occur and,

2 consequently, the limitation of the amplitude is independent of this negative feed-back.

One form of the circuit-arrangement according to the invention will be explained, by way of example, with reference to the accompanying drawings.

Figure 1 shows the embodiment of an oscillator.

Figure 2 shows the embodiment of a selective amplifier.

In the circuit-arrangement shown the discharge tube I is constructed as a pentode. The control-grid circuit of the tube comprises a tuned circuit 2 and a not-decoupled resistance 3, which is included in the cathode lead common to the anode-, control-grid and screen-grid circuits and from which the negative feed-back for all frequencies is taken.

The anode lead comprises an inductance 4 which is coupled to the coil 5 of the circuit 2 in such manner that positive feed-back occurs between the control-grid circuit and the anode circuit.

Between the screen-grid circuit and the control-gricl circuit occurs negative feed-back which is brought about with the aid of the coupling between the coil 6 in the screen-grid circuit and the coil 5.

If, moreover, the resistance 1, which is also included in the cathode lead, is short-circuited with the aid of a switch 8, the circuit-arrangement operates as an oscillator with which the suppressor grid of the tube is connected to the cathode.

The anode circuit furthermore comprises a resistance of a value such that with an increase of the grid alternating-voltage of the tube before the grid becomes positive or, on the other hand, becomes more negative than the cut-off point of the grid-voltage anode-current characteristic curve, which likewise would lead to limitation of the amplitude of the anode alternating voltage, a current of such a value occurs in the anode circuit that transfer of current into the screengrid circuit takes place, owing to which the selective negative feed-back increases and the selective positive feed-back of the anode circuit decreases.

With this circuit-arrangement the amplitude of the anode alternating voltage is therefore limited owing to the current distribution'whichoccurs. I

,By varying the resistance 3, the frequency stability may be controlled without exerting'any influence on the limitation of the amplitude of the anode alternating voltage.

If the switch 8 is opened, it is possible to realize, with a proper choice of the resistance I, an amplifying system with which, consequently, oscillation does not occur but selective amplification of voltages of a frequency equal to that of the tuned circuit 2 will take place. In this system the suppressor grid is decoupled from the cathode and the signal to be amplified is supplied to input terminals I and II of the suppressor-grid circuit shown in Figure 2.

This circuit-arrangement also affords the ad-.

vantages of limitation independent of negative feed-back as referred to above with respect to the oscillator circuit-arrangement.

It may finally be observed that with this circuit-arrangement, either operating as an oscillator or as a selective amplifier, the amplitude of the anode alternating voltage produced is substantially insensitive to variations of the. resistance 9. If, for example, this resistance is decreased, the alternating-voltage amplitude in the anode circuit tends to decrease, owing to which, however, the positive feed-back would increase and the negative feed-back in the screen-grid circuit would decrease with the result that the initial amplitude is restored.

What we claim is:

1. An electronic circuit arrangement comprising an electron discharge tube having a cathode, first and second grids and an anode, a resonant circuit coupled between said first grid and said cathode and tuned to a predetermined frequency, a selective positive-feedback path between said anode and said first grid, a selective negative-feedback path between said second grid and said first grid, said selective paths being operative at the frequency of said resonant circuit, and a negative-feedback impedance interposed between said cathode and said resonant circuit, said impedance being nonselective.

2. An electronic circuit arrangement comprising an electron discharge tube having a cathode, first and second grids and an anode, a resonant circuit coupled between said first grid and said cathode and tuned to a definite frequency, selective positive-feedback means including a first coil connected to said anode and inductively coupled to said resonant circuit, selective negative-feedback means including a second coil connected to said second grid and inductively coupled to said resonant circuit, said selective feedback means operating at the frequency of said resonant circuit, and a negative-feedback impedance interposed between said cathode and said resonant circuit, said impedance being non-selective.

3. An electronic circuit arrangement comprising an electron discharge tube having a cathode, first and second grids and an anode, a resonant circuit coupled between said first grid and cathode and tuned to a definite frequency, a first coil coupled between said anode and said cathode, said first coil being inductively coupled to said resonant circuit to produce selective positive-feedback at said frequency, a second coil coupled between said second grid and said cathode, said second coil being inductively coupled to said resonant circuit to produce selective negative-feedback at said frequency, and a non-selective negative-feedback resistance interposed between said cathode and said resonant circuit, said first coil and said second coil.

4. An electronic circuit arrangement, as set forth in claim 3, further including a resistor interposed between said first coil and said cathode and having a value at which the amplitude of the anode voltage is limited to decrease the selective positive-feedback whereby the amplitude of the second grid voltage is correspondingly raised to increase the selective negative-feedback.

5. An electronic circuit arrangement comprising an electronic discharge tube having a cathode, a control grid, a screen grid and an anode, a negative-feedback resistance, a resonant circuit tuned to a definite frequency and having one end connected to said control grid and the other end connected to said cathode through said negative-feedback resistance, a first coil, a source of anode potential having its positive end connected through said first coil to said anode and its negative end connected through said negativefeedback resistance to said cathode, said first coil being inductively coupled to said resonant circuit to produce selective positive-feedback at said frequency, a second coil connected between said screen grid and the positive end of said source, said second coil being inductively coupled to said resonant circuit to produce selective negative-feedback at said frequency, and a resistor interposed between the positive end of said source and said first coil and having a value at which the amplitude of voltage on said anode is limited to effect a corresponding increase in the amplitude of voltage on said screen grid.

6. An electronic oscillator circuit arrangement comprising an electronic discharge tube having a cathode, a control grid a screen grid, a suppressor grid and an anode, a negative-feedback resistance, a resonant circuit tuned to a definite frequency and having one end connected to said control grid and the other end connected to said cathode through said negative-feedback resistance, a first coil, a source of anode potential having its positive end connected through said first coil to said anode and its negative end connected through said negative-feedback resistance to said cathode, said first coil being inductively coupled to said resonant circuit to produce selective-positive feedback at said frequency, a second coil connected between said screen grid and the positive end of said source. said second coil being inductively coupled to said resonant circuit to produce selective negativefeedback at said frequency, and a resistor interposed between the positive end of said source and said first coil and having a value at which the amplitude of voltage on said anode is limited to effect a corresponding increase in the amplitude of voltage on said screen grid, said suppressor grid being connected to said cathode.

'7. An electronic amplifying circuit arrangement comprising an electronic discharge tube having a cathode, a control grid, a screen grid, a suppressor grid and an anode, a negativefeedback resistance, a resonant circuit tuned to the frequency to be amplified and having one end connected to said control grid and the other end connected to said cathode through said negative-feedback resistance, a first coil, a source of anode potential having its positive end connected through said first coil to said anode and its negative end connected through said negative-feedback resistance to said cathode, said first coil being inductively coupled to said resonant circuit to produce selective positive-feedback at said frequency, a second coil connected between said screen grid and the positive end of said source, said second coil being inductively coupled to said resonant circuit to produce selective negative-feedback at said frequency, a resistor interposed between the positive end of said source and said first coil and having a value at which the amplitude of voltage on said anode is limited to efiect a corresponding increase in the amplitude of voltage on said screen grid, and an input circuit connected to said suppressor grid to apply oscillations to be amplified to said circuit.

JOHANNES ANTON GREEFKES.

JOHANNES ENSINK.

6 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,243,401 Sturley May 27, 1941 2,268,872 Hewlett Jan. 6, 1942 

